Abstract
Egestion by the amphipod Hyalella azteca (Saussure) decreased as browsing removed flocculent sediment material. Faecal pellet production increased linearly with increasing temperature between 5?C and 20?C and decreased with increasing body size. The weight of single faecal pellets was directly related to amphipod dry weight. These relationships were used to calculate egestion by amphipods of various sizes at different temperatures. On a percentage body weight basis young amphipods egest 3 to 4 times more sediment than do adults. Neither light conditions, time of day, sex nor the presence or absence of eggs influenced egestion rates, but faecal pellet production was lowered during moulting. Ingestion and egestion rates were directly related. Calculations of ingestion from egestion rates and assimilation efficiency compared well with independent measures of sediment intake. Egestion/body weight of various aquatic deposit-feeding invertebrates is compared. Despite variation, the relationship is similar to one described for terrestrial arthropods and indicates that egestion is proportional to body surface area.
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